Increasing energy demand has been driving research to build energy efficient systems to fulfill the needs with energy utilization. Renewable energy such as photovoltaic (PV), wind generation, fuel cell, and tidal energy have started sharing a significant percentage of load demand. Based on end user/load requirements and load demand, different concepts such as standalone renewable systems and hybrid power systems for an alternating current (AC) grid and DC distributed systems (DCDS) have been proposed. Among these, DC grid distributed systems have been gaining popularity because many office buildings, commercial spaces, sports complexes, and conference halls have used a large number of DC loads. Such DC loads include, for example, LED lighting, computers, and printers. DCDS have shown significant improvement in energy efficiency, reliability, and economic savings, leaving far behind AC grid, especially, when integrating renewable energy sources to the distribution systems.
It has been known that lighting load shares a considerable portion of total energy, and in particular, applications such as sports complexes, IT parks, and commercial buildings (CB). CB may use more than 50% of lighting loads. For energy efficient LED lighting, energy saving is about six folds than incandescent, florescent and compact florescent (CFL), and longer lasting than conventional light sources. Further, solid state lighting (LED lighting) tend to be the future in illuminating technology since LED lighting has minimal to no environmental side effects.
DC power supplies have been invariably obtained from an AC-DC converter, which makes use of extra electronic circuitry, increases component count, power loss, and harmonic distortions in the grid. The DC grid voltage level may be regulated according to end load or application. 48V DC voltage for the grid (lower voltages<220) is generally not suitable because the current requirement of the loads will be high which results in thick wiring cords leads some power losses and also generate heat, in overall it is not economic. Further, DC loads do not have reactive power demand, which causes the current rating to decrease in delivering the same amount of power.
Office spaces and commercial buildings generally have about a 40-50% lighting load, and sports complexes and stadiums generally use greater than 50% of lighting loads. Conventional LED drivers are usually based on AC-DC then switched mode DC-DC for every light fixture and the same fixture cannot operate at different power levels (dimmable). These LED fixtures generate the harmonics in the supply system and two levels of converters reduce the efficiency of the overall driver. These also lead to utilization of the capacitors, inductors, drivers for metal-oxide-semiconductor field-effect transistors (MOSFETs) and current controller integrated circuits (IC's), which leads to a higher size of the driver and high cost.
Further, conventional LED drivers consist of switching regulators that employ inductors. Inductors are usually custom made and occupy a significant footprint on the driver printed circuit board (PCB). This becomes a major bottleneck for minimizing a PCB driver footprint for high voltage applications.
There is a need, therefore to provide a power converter that transforms DC to DC with controllable current. There is also a need to provide an LED driver that achieves high voltage operation, and avoids the use of inductors and other large and expensive electronic components, while avoiding electromagnetic interference (EMI) and other issues associated with pulse-width modulation (PWM) dimmers.